An essential oil is made up of numerous chemical molecules, giving it its active ingredients. These components can be divided into 12 large families: terpenes, alcohols, aldehydes, carbides, ketones, coumarins, esters, ethers, lactones, oxides, phenols and finally phthalides.
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The different types of molecules
A odorous molecule is a molecule which, as its name suggests, will have an odor. It should not be confused with the term aromatic molecule, often used by misnomer, and which corresponds to molecules containing an unsaturated cyclic carbon chain (that is to say that there will be double bonds in the cycle, making the molecule very stable). However, most aromatic molecules are odorous, but some odorant molecules are not aromatic, as we will see. In short, a great example of the complexity of chemistry!
Terpenes represent the most widespread biochemical family of essential oils. They are the perfect example of non-aromatic odorous molecules! They are composed only of carbons and hydrogens. In essential oils, we will find monoterpenes, with 10 carbons, sesquiterpenes, with 15 carbons, and to a lesser extent diterpenes, with 20 carbons. Terpene compounds are very varied in essential oils. When functional groups (alcohol, ketone, aldehyde, etc.) are present, we will speak of terpenoids. So, depending on the number of carbons and the functional groups, there will be a multitude of terpenes... Uh terpenoids sorry. Between monoterpenol, sesquiterpene carbide or terpene epoxide, the choice is as dense as it is varied!
As we know, essential oils have a very complex composition. If they were only composed of terpene molecules, that would be known! Indeed, we will also find non-terpene aromatic molecules, such as aromatic aldehydes, or the famous coumarins for example.
Chemical families
Carbides
Activities of monoterpene carbides
Examples : limonene, pinenes, terpinenes, paracymene, sabinene, camphene, beta-phellandrene,...
Main essential oils containing : citrus essences (Lemon, Orange, etc.), Black Spruce, Scots Pine, Cistus, Coriander, Thyme, Mountain Savory, RavintsaraActivities of sesquiterpene carbides
Anti-inflammatory, anti-histamine, spasmolytic, calming.
Examples : beta-bisabolene, alpha-humulene, beta-caryophyllene, D-germacrene...
Main essential oils containing : balsam fir, oregano
Alcohols
Activities of monoterpenols (or monoterpene alcohols)
anti-infectious (bactericidal, virucidal, fungicide, parasiticide), general tonic, immunomodulating, spasmolytic.
Examples: linalool, geraniol, citronellol, terpinen-4-ol, thujanol-4, menthol, borneol...
Main essential oils containing : Thyme, Fine Lavender, Palmarosa, Rosat Geranium, Tea Tree, Shelled Marjoram, Wild Mint...
Sesquiterpenol activity
Tonics, venous and lymphatic decongestant, estrogen-like for some.
Examples: farnesol, elemol, viridiflorol, cedrol, santalol, patchoulol, globulol
Main essential oils containing: Lemongrass, Ylang Ylang, Niaouli, Patchouli, Eucalyptus globulus,...
Aldehydes
Aldehydes come from alcohols, but are present in traces in essential oils. Much more volatile, they are dermocaustic and photosensitive. There are 2 types of aldehydes, terpenes and aromatics.
Aldehyde activities
Anti-infectious (anti-bacterial, antifungal, antiviral) anti-inflammatory, general tonic, calming of the nervous system, immunomodulating, digestive.
Examples of monoterpene aldehydes: citrals (neral and geranial), citronellal
Main essential oils containing: Java Lemongrass, Lemon Eucalyptus, Lemon Balm, Lemon,...
Examples of aromatic aldehydes: cuminic aldehyde, cinnamic aldehyde
Main essential oils containing: Cumin, Cinnamon...
Ketones
Ketones are organic compounds with a double bond between a carbon atom and an oxygen atom. We then speak of a carbonyl group. They present a high risk of toxicity on the nervous system on the one hand, and an abortive risk on the other. Essential oils which contain it should therefore not be used in too high a dose or in repeated doses. To recognize them it's easy, it has a suffix in “one”.
Ketone Activities
Anti-infectious (antifungal, antibacterial, antiparasitic), mucolytic, healing, lipolytic, anti-hematoma, nerve tonic (at low doses), analgesic, anti-inflammatory, cholagogue and choleretic.
Examples: verbenone, thujone, borneone (camphor), fenchone, menthone, carvone, italidiones...
Main essential oils containing: Rosemary with Verbenone, Sage, Rosemary with Camphor, Lavandula Stoechas, Peppermint, Caraway, Italian Helichrysum…
Oxides
Oxides are compounds resulting from the combination of oxygen with another substance. Essential oils include monoxides, dioxides and terpene epoxides. They will have an action on the exocrine glands of the respiratory and digestive mucous membranes.
Oxide activities
Anti-infectious (anti-viral, anti-parasitic, anti-bacterial, antifungal), expectorant, stomachic, carminative, immunomodulating.
Examples : 1,8-cineole (eucalyptol), linalool oxide
Main essential oils containing : eucalyptus, noble laurel, ravintsara, niaouli, cajeput,...
Esters
Monoterpene esters will mainly act at the level of the nervous system, via ion channels, hence the resulting properties.
Ester activities
Antispasmodic, calming, anti-inflammatory, anti-arrhythmic.
Examples: bornyl acetate, linalyl acetate, geranyl formate, neryl acetate, benzyl benzoate...
Main essential oils containing: Siberian Fir, Black Spruce, Clary Sage, Petit Grain Bigarade, Rosat Geranium,...
The ethers
Antispasmodic, anti-allergic, analgesic
Examples: methyl-chavicol, apiol, safrol, myristin
Main essential oils containing: Basil, tarragon, sweet fennel
Lactones
Lactones are characterized by the presence of a ketone function in a ring. As a result, they present the same risks as ketones, they are neurotoxic and abortifacient in high doses, but are much rarer.
Lactone activities
Mucolytic, expectorant, anti-infectious (anti-bacterial and anti-fungal), immunomodulating, antispasmodic, hepatostimulating
Examples: alantolactone, xanthatine, santalolactone, costunolide
Main essential oils containing: Fragrant inula, noble laurel, Roman chamomile, Italian helichrysum...
Phenols
The action of phenols is very powerful, special attention must be paid to their use in order to avoid accidents and side effects. In addition, essential oils containing high doses of phenols are dermocaustic, so skin applications should be avoided.
Activities of phenols
Powerful anti-infectious (bactericidal, virucidal, fungicide, parasiticide), anti-inflammatories, immunomodulating, analgesic, general tonic
Examples: carvacrol, thymol, eugenol
Main essential oils containing: Compact Oregano, Thymol Thyme, Clove, Mountain Savory
Coumarins
Coumarins are indeed aromatic molecules this time. Present in small quantities in essential oils, they are no less powerful! Sensitive to UV, coumarins are photosensitizing.
Coumarin activities
Sedative, nerve calming, spasmolytic, anticoagulant, hypotensive
Examples: bergapten, herniarin, limettine, angelicin...
Main essential oils containing: Cinnamon, bergamot, lemon, lovage, tangerine...
Phthalides
Phthalides are related to coumarins. They have an action on the liver and kidneys by stimulating their elimination action.
Phthalide activity: Anti-infectious (bactericide, fungicide, parasiticide), hepatocyte detoxifier, toning, calming
Examples : Z-ligustilide, z-butylidenphthalide,...
Main essential oils containing: Lovage, Celery
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Bibliography
Work : de la Charie, T. (2019). Treat yourself with essential oils. Why and how does it work? Editions du Rocher.
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About these tips
This aromatherapy article was written by Théophane de la Charie, author of the book “Treat yourself with essential oils”, accompanied by a multidisciplinary team made up of pharmacists, biochemists and agronomists.
La Compagnie des Sens and its teams do not encourage self-medication. The information and advice provided comes from a reference bibliographic database (books, scientific publications, etc.). They are given for information purposes, or to suggest avenues for reflection: they should in no case replace a diagnosis, consultation or medical follow-up, and cannot engage the liability of the Compagnie des Sens.